To cross a stream, highway or valley (where by the hold off due to a flight of locks at either side will be unacceptable) the valley may be spanned by a navigable aqueduct – a well known example in Wales is the Pontcysyllte Aqueduct (now a UNESCO World Heritage https://musicainfantil88765.mybjjblog.com/indicators-on-canal-infantil-you-should-know-49456590